The invention relates to methods and apparatus for receiving and processing multi-channel digital video transmissions such as a digital satellite broadcast receiver that provides quicker perceived response to a user""s command to change channels.
The time required for a conventional multi-channel digital video receiver, such as a direct broadcast satellite (DBS) receiver, to change channels is comparatively greater than the time needed to change channels in a conventional analog system such as an over-the-air television system. In either system, reception processing for a selected broadcast channel requires a tuner to tune to the desired carrier frequency and output the desired programming to an output device such as a video-audio display.
Reception of a digital broadcast typically requires additional process steps. High capacity systems typically utilize signal compression techniques, such as MPEG2 (Moving Pictures Expert Group Standard 2) encoding, as well as effective error correction coding. To receive and process these signals, most digital receivers adjust for the appropriate polarity and frequency of the received satellite transmission, filter and select the required data packets corresponding to the desired broadcast channel selected, and demodulate the channel data including the program and other content. Most digital systems further enable and lock error-correction circuitry into the new channel before transporting the resulting data packets to a digital decoder. For example, in decoding the video data packets in an MPEG stream, the next complete video frame (I-frame) is generally input to memory buffers before video images are re-encoded to an analog signal for display on the user""s screen.
In a high-capacity, multiple-channel digital video system, conventional receivers may therefor require several tenths of a second, for example, from 0.3 to more than 1 second, to change channels.
These delays may be perceived by viewers, particularly viewers acclimated to the more immediate response in analog television systems, and may be particularly annoying to a viewer that is sequentially scrolling through adjacent channels, an operation that many users like to perform quickly.
In light of the numerous processes being performed, the improvements in processing time have previously been obtained only with substantial effort and expenditures to improve the processing time for each of the required processes. However, given the nature of MPEG 2 or similar predictive or bidirectional predictive compression techniques, there are limits on the ability to reduce worst-case acquisition times. Another attempt to reduce the perceived time response utilizes multiple tuners so that channel selection may be made by switching to the output of another tuner that has been previously tuned to a second broadcast channel. However, using additional tuners reduces processing time only to the extent that the desire channel corresponds, predictably, with the selection of those channels that are pre-tuned. Accordingly, multiple redundant tuners may be required when quick sequential scanning of the selected channels and their program content is desired. In addition, multiple tuner receivers do not reduce perceived acquisition time when channel changes do not correspond to a predicted, pre-tuned channel.
A multi-channel digital video receiver and the method that are the subject of this invention provide significantly quicker perceived response to channel changes.
In general, the receiver includes a tuning unit with a tuner module and a decoder unit, although the invention may also be adopted with a multiple tuner receiver to overcome problems discussed above. The receiver practices a method for perceptibly masking acquisition time after selection, by the user, of an alternative signal source. The receiver generates an output for portraying a masking display, either video, audio or both, before the acquisition and processing time has expired.
In a preferred embodiment, a reduced perceived time response is generated by transmitting a simple trigger signal at smaller intervals than the acquisition time period. Such triggering may be transmitted from the signal broadcast location or may be accomplished by locally identifying a source selector change and triggering an image portrayal from a local storage device in response to said identification of source selection change. Triggering may also comprise generating a spoof signal simulating an acquisition complete signal.
As a result, the present invention provides improved perceived response to channel selection changes without the complex and expensive improvements needed to improve actual acquisition time. Moreover, the system is substantially less expensive than, and can be used to supplement and improve the operation of, previously known multiple channel receivers.